Aircraft Nose Landing Gear

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The responsibilities of a ground crew team carrying out an aircraft tow include ensuring that no part of the aircraft structure will impact any fixed object, vehicle, or other aircraft. The ground crew should have intercom communication with the personnel on the flight deck and both parties should be able to listen to communications with ATC.

Aircraft Nose Landing Gear

In the absence from the flight deck of a pilot qualified on the aircraft type, The person in charge of the ground vehicle carrying out the tow will usually be responsible for obtaining any necessary ATC aircraft movement clearances.

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This increases the tail clearance and allows a higher nose-up angle (9 degrees) for the same takeoff speed. Not only does this increased tail clearance reduce the risk of a tail strike, the higher nose angle means that the aircraft doesn't have to accelerate to a faster speed in order to takeoff.

In order to do this, before an aircraft is certified for flight, the gear must undergo a test known as the drop test. Here, manufacturers drop the gear to simulate forces experienced in not only normal and testing conditions, but also those well beyond what the aircraft might ever expect to encounter.

All takeoff performance is done assuming that an engine will fail at the critical moment of takeoff. If this happens, how the pilots rotate the nose into the air is absolutely crucial. Rotate too slowly and the aircraft may not get airborne before the end of the runway.

Rotate too quickly and the aircraft may be flying too slowly to climb safely away from the ground. On 13 November 2008, a Boeing 737-800 with an unserviceable APU was being operated by Ryanair on a passenger flight at night was in collision with a tug after a cross-bleed engine start procedure was initiated prior to the completion of a complex aircraft pushback in rain.

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As the power was increased on the No 1 engine in preparation for the No 2 engine start, the resulting increase in thrust was greater than the counter-force provided by the tug and the aircraft started to move forwards.

The towbar attachment failed and subsequently the aircraft's No 1 engine impacted the side of the tug, prior to the aircraft brakes being applied. At this point the brakes can begin to take effect, slowing the aircraft to a safe stop.

When the runway is wet or slippery, pilots will try to make a firm touch down to get the brakes working as soon as possible. "I didn't even realize we'd landed!" Of all the comments pilots like to receive from passengers, this has to be right up there.

Everyone loves a smooth landing, it makes us pilots feel proud and passengers feel safe. The credit card offers that appear on the website are from credit card companies from which ThePointsGuy.com receives compensation. This compensation may impact how and where products appear on this site (including, for example, the order in which they appear).

The Procedure

This site does not include all credit card companies or all available credit card offers. Please view our advertising policy page for more information. This consists of a dedicated DC-powered electric pump and fluid from the center hydraulic system to extend the gear.

Selecting the alternate gear switch to the down position releases the gear doors and locks which locks the gear in the up position. Once the person in charge on the flight deck of the aircraft has given their confirmation of 'brakes released' to the person in charge of the ground crew vehicle who are to carry out the tow, the ground crew become responsible for the safe maneuvering of the aircraft in accordance with any ATC Clearance which may be required and as may have been specifically agreed beforehand.

When airborne, to reduce drag, the gear is retracted and folded away into the belly of the aircraft, waiting to be used for landing. However, leaving the retracted gear exposed to the elements would still create a large amount of drag, drastically increasing both fuel usage and noise.

To stop this from happening, the gear bays have doors. On 27 September 2017, an Airbus A320 being maneuvered off the departure gate at Dublin by tug was being pulled forward when the tow bar shear pin broke and the tug driver lost control.

Wheels And Doors

The tug then collided with the right engine causing significant damage. The tug driver and assisting ground crew were not injured. The Investigation concluded that although the shear pin failure was not attributable to any particular cause, the relative severity of the outcome was probably increased by the wet surface, a forward slope on the ramp and fact that an engine start was in progress.

During WW2, hundreds of accidents were attributed to pilots inexplicably raising the landing gear just before landing. On closer study, it was found that instead of lowering the flaps for landing, pilots were instead raising the landing gear.

Why? To absorb the shock of the landing impact, the landing gear has an oleo strut, which acts as a type of suspension. This uses a mix of compressed air and hydraulic fluid to dissipate the forces experienced on landing across the airframe and also to dampen any recoil to reduce the chances of the aircraft bouncing back up into the air.

The landing gear system on the 787 Dreamliner consists of two main landing gear assemblies and one nose gear assembly. Each main gear set up has four wheels, each of which has an electronic brake. The nose gear has two wheels, neither of which have a brake.

Early Gear Door Opening

To improve aircraft performance on the 787-9 and 787-10, one second after the aircraft detects that it is airborne, the main landing gear doors automatically open. This happens even before the pilots select the landing gear lever to the up position.

This action may seem random but it is done quite deliberately. Longer aircraft are great. Manufacturers can stretch an original aircraft design and create a load more space for passengers and cargo and this can often be done without a complete redesign.

A great example of this is when Boeing took the original 787-8 and stretched it by 20 feet to create the 787-9. The landing gear lever in the flight deck is situated on the center panel within easy reach of both pilots.

If you look closely, you'll notice that it's actually in the shape of a wheel. This is not by accident. Aircraft can experience severe loads on touchdown so they need landing gear strong enough to take this impact.

Preventing Tail Strikes

Through rigorous design and testing, the gear on commercial aircraft can take far more force than any pilot could ever inflict on them during a normal landing. One of the worst fears some passengers have is the landing gear not coming down for landing.

Whilst problematic, like all systems onboard the aircraft, there is a backup to the main system should it not work properly. To hit the sweet spot in between these two extremes, pilots must rotate the nose up to a line projected in the head-up display called the "TOGA reference line."

Once there, and the aircraft is stable, we can then transfer back to normal guidance. The function of any flight deck occupant(s) is likely to be the appropriate operation of the aircraft braking system and the provision of sufficient aircraft electrical power to operate the radio and appropriate external and internal lighting.

It is likely that where available, an APU will be running to provide electrical power and that hydraulic accumulator pressure for braking will be achieved by use of an electrical pump. The ‘traditional’ method of allowing the ground vehicle to move an aircraft is to attach it to the aircraft nose landing gear by means of a towbar.

Operating The Landing Gear

These must be approved for use with a particular aircraft type and clearly marked as such since there is no universal towbar specification. An alternative method which is becoming more common for towing is the use of a specialized vehicle called a 'towbarless tug'.

This positions two low level 'arms' either side of the aircraft nose landing gear and these are used to engage with the aircraft gear leg and raise it slightly off the ground. On 13 January 2016 ice was found on the upper and lower wing surfaces of a Boeing 777-300ER about to depart in the late morning from Lisbon in CAVOK conditions and 10°C.

As Lisbon had no de-ice facilities, it was towed to a location where the sun would melt the ice more quickly but during poorly-planned maneuvering, one of the wingtips was damaged by contact with an obstruction.

The Investigation attributed the ice which led to the problematic re-positioning to the operator's policy of tankering most of the return fuel on the overnight inbound flight where it had become cold-soaked. When the aircraft detects that it is on the ground, the spoilers will deploy.

Bottom Line

These large surfaces on the top of the wing dump any remaining lift, dropping the weight of the aircraft onto the wheels. On liftoff, the tires will be spinning at around 180mph. Bringing them up inside the aircraft at this speed could cause some serious vibration to be felt in the passenger cabin.

As a result, before the wheels are folded away, the brakes on the main wheels are applied to stop them from spinning. The forward movement of an aircraft, usually with engines off, using the power of a specialized ground vehicle attached to or supporting the nose landing gear.

It may occur for the movement of both in service and out of service aircraft. This will affect the promulgation of procedures and the required qualification for those occupying the flight crew seats on the aircraft during the manoeuvre.

As part of out of service repositioning of aircraft supervised by maintenance personnel, it may follow the Pushback from a nose-in gate of an empty aircraft with engines off. On 4 June 2002, the crew of an MD82 in the cruise at FL330 with AP and A/T engaged failed to notice progressive loss of airspeed and concurrent increase in pitch attitude as both engines rolled back to thrust levels which could not sustain level flight.

What If The Wheels Dont Come Down?

The aircraft stalled and a recovery was accomplished with significant altitude necessary before engine thrust was restored and a diversion made. The Investigation attributed the engine rollback to ice crystal icing obstructing the engine inlet pressure sensors following crew failure to use the engine anti-icing as prescribed.

Two Safety Recommendations were made. As the gear uses gravity to deploy in normal operation, the only thing hindering them is the gear doors, which are powered hydraulically. Should there be a problem with the normal system, we can use the alternate extension system.

On the -9 and -10, the early gear door opening eradicates this problem as the initial pitch angle we must fly does not change. This makes for a much more straightforward and easier maneuver to fly.

Ground Crews must be specifically made aware of both these risks and must be fully trained on both ATC practices and the towing of the particular aircraft type involved. The later should include awareness of aircraft dimensions and turning arcs.

Air-Ground Sensing System

The reason for this maneuver is to increase the angle which the oncoming airflow hits the wings, known as the angle of attack. In those few seconds, the speed of the air over the wings, combined with the change of angle of attack, enables the aircraft to lift off the runway.

So, when Boeing created the even longer 787-10, (40 feet longer than the 787-8), it ran into a problem. When pilots reach a certain speed during the takeoff run, we gently pull back on the control column.

This causes the tail of the aircraft to sink lower, using the landing gear as a pivot to raise the nose into the air. Certain systems only work on the ground, and others in the air.

As you'd hope, the landing gear lever will not allow the gear to move to the up position when the aircraft is on the ground. So how does the aircraft know where it is?

Built For A Pounding

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